1. Field of the Invention
The present invention relates to a surface acoustic wave device having an interdigital transducer (hereinafter referred to as IDT) disposed on a surface acoustic wave substrate and, more particularly, to a surface acoustic wave device using Love waves.
2. Description of the Related Art
A variety of surface acoustic wave devices utilizing surface acoustic waves have been proposed. For example, the Technical Report of the Institute of Electronics, Information and Communication Engineers (IEICE), pp. 7-14, US 82-35, 1982 discloses a surface acoustic wave device in which a thin layer of a slow acoustic speed material is formed on a rotational Y-cut, X-propagated LiNbO.sub.3 substrate, wherein a pseudo surface acoustic wave produced therein is a Love-wave type surface acoustic wave which is free from transmission attenuation.
The Technical Report of Institute of Electronics, Information and Communication Engineers, pp. 31-38, US 86-37, 1986 discloses a rotational Y-cut, X-propagated LiNbO.sub.3 substrate, which has no single uniformly arranged film disposed thereon but has metal strips intermittently arranged thereon to generate Love waves.
Japanese Laid-Open Patent Publication No. 63-260213 discloses a surface acoustic wave device which uses Love waves and which comprises a rotational Y-cut, X-propagated LiNbO.sub.3 substrate having an IDT constructed of a heavy metal such as gold, silver, or platinum.
Japanese Laid-open Patent Publication No. 8-125485 discloses a surface acoustic wave device which uses Love waves and which comprises an IDT constructed of tungsten or tantalum, provided on a surface acoustic wave substrate.
Japanese Laid-Open Patent Publication No. 8-250966 discloses a surface acoustic wave device which uses Love waves and which comprises an IDT of two layers of Ta/Al provided on a surface acoustic substrate.
Although Technical Reports US 82-35 and US 86-37, and Japanese Laid-Open Patent Publication No. 63-260213 describe that the surface acoustic wave device has an IDT constructed of gold, silver or platinum, the device which was actually tested is a gold IDT. To generate the Love wave, the use of the abovedescribed heavy metals having large mass is thought to be required, but the use of a heavy metal is very costly.
According to Japanese Laid-Open Patent Publication No. 8-125485, the IDT is constructed of Ta or W, which are less costly than gold and which provide a low Q factor and a relatively high specific resistance, and can still work in a resonator but experiences great difficulties and disadvantages when used in a filter.
According to Japanese Laid-Open Patent Publication No. 8-250966, the IDT is constructed of a two-layered structure of Ta/Al, resulting in a decreased specific resistance. Even with the IDT of the two-layered structure of Ta/Al, the specific resistance is not sufficiently low, and satisfactory performance is not achieved when such a configuration is used as a filter.